Legal philosophers have given relatively little attention to international law in comparison to other topics, and philosophers working on international or global justice have not taken international law as a primary focus, either. Allen Buchanan's recent work is arguably the most important exception to these trends. For over a decade he has devoted significant time and philosophical skill to questions central to international law, and has tied these concerns to related issues of global justice more generally. In what follows I review Buchanan's new collection of essays, Human Rights, Legitimacy, and the Use of Force, paying special attention to Buchanan's argument that the philosophy of international law must be more empirically informed than it has been so far, and also to his claim that greater emphasis must be placed on the role of institutions. While these are important claims, I show that Buchanan often does not take the first far enough, and that appealing to institutions cannot do as much as Buchanan hopes or needs if his substantive conclusions are to be correct.